1. Field of the Invention
This invention relates to a method and system to facilitate phytoremediation, especially to permit phytoremediation to be conducted at depths beyond those traditionally employed.
2. Description of the Related Art
U.S. Pat. No. 5,829,192 utilizes a tree in order to have its root system aid in the remediation of contaminated soil and groundwater, which constitutes phytoremediation.
The only step in the process of that patent which differs from the normal planting of a tree is, however, is xe2x80x9cproviding a casing made of material which is impervious to water and nutrients for root growth, and lining the walls of the hole [in which the tree is planted] with such casing . . . xe2x80x9d
The purpose of the casing is stated to be xe2x80x9cso that root growth is inhibited from growing outside of the prepared hole.xe2x80x9d
However, no provision is made to encourage root growth below the depth at which roots are normally produced.
Phillip Craul wrote in Urban Soil in Landscape Design (1992) that xe2x80x9c[m]ost roots occur within the surface 3 ft. (1 m) of . . . soils . . . as the result of . . . proximity of favorable root growth conditions . . . xe2x80x9d
But the critical need for rooting at depths below 3 feet for trees employed in phytoremediation is evident from the facts that contaminants often exist or extend below such depth and that the greatest potential for contamination of drinking water occurs at lower depths.
Previous attempts to encourage deep rooting have mistakenly only considered the need of trees for nutrients and water.
The present invention, however, recognizes that favorable growth of root systems requires aeration, gaseous exchange, and decreased soil compaction in addition to nutrients and water.
Besides providing the preceding, the present invention has appreciated the fact that the germination and growth of mycorrhizae spores not only creates macro pores through which root hair can pass, but the fungus resulting from such germination and growth also creates a pathway for nutrients to reach the root hair.
Furthermore, the present invention optionally directs forced air to deep areas where it is desired to establish root systems. Such forced air also opens macro pores in soil.
Additionally, to encourage root growth in desired areas, the trunk can be coated in those areas with either vitamin B1 or mycorrhizae spores or a combination of these substances. And in order to create optimal growing conditions in areas at various elevations along the trunk, these areas can be separated by horizontal clay layers. The clay layers preclude oxygen from drifting to the top of the hole in which the tree has been planted and preclude water nutrients from flowing to the bottom of the hole. (Of course, air, nutrients, and water will be supplied to each region between clay layers.)
Similarly, to prevent growth in specific areas, either (a) the trunk can be wrapped with epdm rubber or a biobarrier or (b) the region around the trunk in such areas can be backfilled with gravel so that it will contain no nutrients or water together with an overabundance of air or (c) both techniques can be implemented.
The preceding technologies enable the hole where the tree is planted to be deeper than previously possible and, therefore, enable the tree to perform phytoremediation much farther below grade than has been achieved prior to development of the present invention.